1. Field of the Invention
The present invention relates to an image input apparatus that inputs image information using a 4-line CCD sensor, and an image processing method.
2. Description of the Related Art
A conventional 3-line CCD sensor having three line sensors for RED, GREEN and BLUE has been used to read a color image. The 3-line CCD sensor is configured such that color filters of RED, GREEN and BLUE are disposed on light-receiving surfaces of the respective three line sensors, and the three line sensors are arranged in a one-dimensional fashion. Thus, one location on an original cannot be read at the same time by all the line sensors. A resultant displacement in the original scan direction is corrected by performing position correction for image signals read by the respective line sensors, with use of a memory circuit comprising, e.g. a line memory.
Recently, a 4-line CCD sensor having a 4-line architecture has been marketed as a product. The 4-line CCD sensor is configured such that a monochromatic line sensor for reading a monochromatic image, which has no color filter on its light-receiving surface, is added to the aforementioned 3-line CCD sensor for reading a color image.
Jpn. Pat. Appln. KOKAI Publication No. 2003-87556 discloses a technique wherein a monochromatic original is read with a high resolution and a color original is read with a high sensitivity. In this technique, the light receiving areas of pixels are made different between a line sensor for reading a monochromatic image and three line sensors for reading a color image.
However, this CCD line sensor comprises the line sensor for reading a monochromatic image and the three line sensors for reading a color image and, compared to the line sensor for reading a monochromatic image, the three line sensors for reading a color image are unable to read one location on the original at the same time, as mentioned above. Consequently, color overlapping of a black character becomes difficult when the magnification for reading is changed or non-uniformity occurs in reading speed.
When the color original is read with high sensitivity by making the light receiving areas of pixels different between the line sensor for reading a monochromatic image and the line sensors for reading a color image, the resolution of the color original lowers. Although the resolution can be increased by simple linear interpolation, reproduction of a fine character is degraded by linear interpolation in the prior art.